1. Field of the Invention
The present invention relates to a radar apparatus used, for example, in collision prevention systems in automotive vehicles.
2. Description of the Related Art
As an essential component of, for example, a collision prevention system for automotive vehicles, radar apparatuses for automotive vehicles that detect the distance to an object such as an automotive vehicle in front or an oncoming automotive vehicle are being developed. Recently, electronic scanning-type and mechanical scanning-type radar apparatuses are being developed that can detect not just the distance to the object, but the direction of an object seen from one""s automotive vehicle.
The electronic scanning-type radar apparatus is structured so as to have a plurality of adjacent antenna apparatuses, arranged with their orientations slightly offset, that transmit beams in different directions and receive the reflected waves. For each antenna apparatus, emission and reception of the beams offset in time are carried out in sequence. Thereby, whether or not reflected waves are generated is detected by any antenna, which is to say, from any direction. Not only this multi-beam time-sharing type radar, but also the mechanical scanning-type radar, which mechanically biases the orientation of the transceiver antennas, can detect the direction of the object producing the reflected waves.
In Japanese Patent No. 2567332 (corresponding U.S. Pat. No. 5,448,244) of the present applicants, for example, a method is disclosed wherein weighted equalization processing of the reception levels of the reflected waves in each direction is carried out, and the direction of the object that generated the reflected waves is detected with high precision. As a result of the increased space resolution in two dimensional space, this kind of scanning-type radar apparatus for an automotive vehicle not only detects whether or not there is an obstruction, but detects the approximate shape and dimensions of the obstruction, analyzes them with a computer, and carries out more precise automatic determination of traffic safety.
For example, the next goal will be automatically determining whether or not an automotive vehicle at an angle in front (in the adjacent lane) travelling forward can be passed safely, without a rear end collision or contact, by combining a high resolution radar apparatus and a computer. That is, referring to FIG. 10, the reflected waves generated at the plurality of locations on the automotive vehicle travelling in front at an angle to one""s automotive vehicle are detected by a scanning-type radar apparatus mounted on near the front of one""s automotive vehicle.
The direction of each reflected location that generated reflected waves is detected from the direction of emission of the beams, and the distance to each of location is detected by the time from the emission of the beam to the reception of the reflected wave. In addition, the level of the received signal of the reflected wave generated at each reflected location is indicated by the size of the black circle shown at each of the reflected locations. When weighted equalization processing is carried out for the direction and distance of each reflected location based on the level of the received signal of the corresponding reflected wave, the position of the center of gravity, indicated by the star-shaped mark, is detected. This center of gravity represents the position of the object.
As shown in FIG. 10, in the case of an automotive vehicle at an angle in front travelling forward is running in the same direction as one""s automotive vehicle, as a result of detecting the position by the radar apparatus based on calculating the center of gravity, the computer determines if is possible to pass or edge past based on the approximate width of one""s automotive vehicle and the other automotive vehicle. However, as shown in FIG. 11, in the case that the direction of travel of the automotive vehicle at an angle in front travelling forward is crossing the direction of travel of one""s automotive vehicle, the possibility of edging past cannot be determined only from the result of calculation of the position of the center of gravity described above and the widths of one""s automotive vehicle and the other automotive vehicle.
In this connection, as an example of a countermeasure for the case that the direction of travel of the automotive vehicle in front, as described above, is different from that of one""s automotive vehicle, the employment of the method of determination as shown in FIG. 12 has been conceived. In this method, a line perpendicular to the direction of travel of one""s automotive vehicle is drawn from the location detected to be nearest to one""s automotive vehicle, and at the same time, a line parallel to the direction of travel of one""s automotive vehicle is drawn from the location detected to be farthest from one""s automotive vehicle. The intersection of the perpendicular and parallel lines is detected, and serves as the location nearest to one""s automotive vehicle, and includes a margin (the degree of clearance for safety).
In addition, the safety of passing is determined from the nearest location detected in this manner and the width of one""s automotive vehicle. In the case that passing is unsafe, a warning is issued to the driver. This is the also identical to the case that there is a structure such as a guard rail, instead of the above-described automotive vehicle, in front.
In the method of detection of an object at an angle in front is explained referring to FIG. 12, there is the problem that the margin becomes extremely large, and cannot be put into practical use, in the case that the automotive vehicle in front has a large total length, such as a truck. Therefore, it is an object of the present invention to provide a radar apparatus that detects more accurately the necessary points in a determination related to the safe travel of one""s automotive vehicle among objects such as automotive vehicles at an angle in front travelling forward and structures.
Another object of the present invention is to provide a radar apparatus that can precisely detect the profile of an object at an angle that is crossing the direction of travel of one""s automotive vehicle.
The radar apparatus of the present invention for solving the above-described problem in the conventional technology provides a reflected location detection device that detects the generation source of the reflections (referred to hereinafter as the xe2x80x9creflected locationsxe2x80x9d) for each of a plurality of directions, a device that groups each of the detected reflected locations into groups of singular or plural reflected locations assuming them to be included in an identical object, and a device that detects the reflected location having shortest distance from one""s automotive vehicle among the grouped reflected locations to serve as the reference point related to the safe travel of one""s automotive vehicle.
The radar apparatus of the present invention for solving the problems in the above-described conventional technology provides a reflected location detection device that detects the generation source of the reflections for each of a plurality of directions, a device that groups each of the detected reflected locations into groups of singular or plural reflected locations assuming them to be included in an identical object, and a line segment extraction device that extracts from the arrangement of the grouped reflected locations line segments that form a profile of the object.
The radar apparatus of the present invention for solving the problems in the above-described conventional technology provides are a reflected location detection device that detects the reflected locations for each of a plurality of directions, and an unnecessary data elimination device that detects from among detected reflected locations the reflected locations having a lower reception level, equal to or greater than a predetermined value, than the reflected locations detected as reflected locations having an identical distance in single of plural adjacent directions, and the reflected locations having the reception level lower than a pre-determined threshold value in these directions are considered unnecessary data in these directions.